As dermatologists, we observe cutaneous mosaicism on a daily basis. Individuals begin life with a single genome, and initially all subsequent dividing cells have that identical genome. Mosaicism occurs when a genetic mutation develops in a single cell, which then proliferates into a clonal population. When this mutation occurs during development, it may result in a segmental birthmark, such as an epidermal nevus or capillary malformation. Depending on the cell of origin and timing during development, internal organs may also develop structural anomalies. When a mosaic mutation is acquired later in life, it can result in the development of a benign growth or malignant tumor. The genetic underpinnings of birthmarks and acquired skin lesions are becoming increasingly elucidated. It has been fascinating to discover that the majority of the mutations in congenital and acquired skin lesions occur in oncogenes, yet only a subset develop malignant tumors.
Siegel DH. Cherry Angiomas—Further Expanding the Phenotype With Somatic GNAQ and GNA11 Mutations. JAMA Dermatol. Published online January 02, 2019. doi:10.1001/jamadermatol.2018.4157
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